1. Field of the Invention
This invention relates generally to window sash balancers for use with slide-out sash windows, double-hung sash windows or the like.
2. Prior Art
Window sash balancers to which the invention relates are of the type including a spirally grooved drum of a frustoconical shape around which there is wound in the spiral groove a cord having one end fixed to the drum and the other end secured to the top end of the window sash, which top end is guided for sliding movement along the vertical guideway of a window outer frame in which the window sash is mounted. The drum is provided with and urged by a spiral coiled spring in a direction to resist the rotation of the drum as the latter is rotated about its own axis by the cord when the latter is pulled downwardly by the window sash, thereby balancing the window sash with respect to the window outer frame under the tension of the cord. Heretofore, the above-mentioned spiral groove of the balancers has been formed circumferentially in the drum body by machining or casting, and therefore adjacent groove threads provide a fixed pitch therebetween which in turn limits the use of each balancer to a window sash of a given weight. This has led to the drawback that when it is necessary to use window sashes having different weights, the balancers must have as many different cast or machined grooves as there are sashes. Furthermore, the prior art balancers of this type are difficult to manufacture with increased rate of production on account of the necessity of machining or casting of the grooved drums and hence very costly.